As the number and complexity of wireless applications grow, there is increasing need for circuits designed to operate at high frequencies, i.e., in the RF and microwave frequency range (300 kHz to 300 GHz) for audio, visual, and data transmissions. Circuit materials are needed which combine low dielectric and conductor losses in this frequency range. In particular, a high dielectric constant (K>15) has been required to reduce device size and/or increase capacitance density. Low temperature co-fired ceramic (LTCC) tape is a well-known technology for combining a high conducting metallization (silver and gold) with reliable ceramic dielectric layers for dense packaging of IC circuits. The LTCC tape has been used as a ceramic substrate for multilayer interconnects incorporating various passive components. The majority of present LTCC systems are composed of glass and ceramic filler. Glass is an important part, giving specific functions such as high K and low loss at high frequency. Ceramic fillers usually impart high strength and dimensional stability.
The present invention provides new glass chemistries that exhibit a high dielectric constant (K>15). The resultant glass-ceramic body after firing exhibits good strength with silver and gold compatibility. In addition, the new glasses allow for low temperature firing, i.e., below the melting point of silver which broadens the processing latitude of existing systems.